Polyurethane foams are widely employed in the manufacture of a variety of products and, depending on the end use, can be tailor made to fit the particular application and desired physical properties. For example, high resilience (HR) foam is widely used in furniture, mattresses, automotive and numerous other applications. It is differentiated from conventional foam by its higher comfort or support factor and higher resilience. Specific guidelines have been set forth in ASTM Method D3770 for defining HR foams; however, in practice a much wider class of foams are described by this terminology and the present invention is intended to encompass this broader classification.
High resilience slabstock foam formulations employed commercially typically contain (1) a polymer polyol consisting of a polymer stably dispersed in a reactive ethylene oxide end-capped polyol having more than 50% primary hydroxyl groups; (2) water; (3) a low molecular weight crosslinker/extender, usually diethanolamine (4) a polyether-silicone copolymer stabilizer; (5) amine and tin catalysts; (6) toluene diisocyanate and miscellaneous other additives such as fillers, flame retardants, blowing agents and the like.
Molded high resilience foam can usually be made from high resilience slabstock systems by altering the catalyst compositions; the slabstock foam usually being made with significantly more tin catalyst than is desirable for processing molded foam. Slabstock foam is made almost exclusively with toluene diisocyanate isomer blends while blends of polymeric methylene diisocyanate and toluene diisocyanate are sometimes used for molded foam.
Typical unfilled and water-blown high resilience slabstock foams made commercially range from about 1.8 to 3.5 pounds per cubic foot (pcf) while those containing physical blowing agents are generally less than about 1.8 pcf. Loads (25% IFDs) range from about 20 to 80 pounds per 50 square inch for water blown foams down to 7 to 20 pounds per 50 square inch for foams containing physical blowing agents such as chlorofluorocarbons. Prior to the present invention, production of low density (less than about 1.8 pcf) and/or low load (less than 20 pounds/50 square inch) HR slabstock grades without physical blowing agents had been limited due to little or no processing latitude for the formulations necessary to make these grades.
The processing latitude of commercial HR slabstock foam is usually characterized by the diethanolamine (DEOA) and index ranges that give acceptable processing. A broad range is desirable for not only processing but also grade flexibility since load decreases as the DEOA level increases and index is decreased. The lower DEOA limit is characterized by excessive settle or collapse while, at the upper limit, the foam will show shrinkage (excessive tightness). For a typical commercial polymer polyol, the DEOA latitude will depend on factors such as isocyanate index, water level, catalyst types/levels, surfactant and machine parameters. In general, it becomes difficult to find a DEOA level that will yield stable and non-shrinking foam at water levels higher than about 3.2 and/or indices above 115 and below 100. This results in more off-grade production and increased manufacturing costs.
Although a wide variety of methods and polyurethane formulations have been reported in the patent literature, to date none has disclosed nor taught the polymer polyol compositions and formulations of the present invention.
Polymer polyols in which the polyols contain 3 to 10 percent ethylene oxide, have an equivalent weight greater than 1250 and have average functionality greater than 3.2 have been reported in U.S. Pat. No. 4,111,865 and are indicated to yield flexible foams with improved static fatigue and humid sensitivity. However, free-rise foams made with these compositions were tight and exhibited shrinkage.
U.S. Pat. No. 3,857,800 and British Patent No. 1,339,442 disclose the use of a subsidary polyol high in poly(oxyethylene) in conjunction with a polyoxyethylene capped oxypropylene polyol, wherein the subsidary polyol assists in opening the foam cells to avoid shrinkage. Examples are provided in which a crosslinking agent was used but no disclosure related to the use of polymer polyols was indicated. All commercially useful systems for producing high resilience foam rely on polymer polyols; whereas the stably dispersed polymer component provides shrinkage resistance. Ommission of polymer polyol from HR foam formulations employing catalyst combinations that yield commercially acceptable cure rates and silicone surfactants yielding acceptable cell structure results in severe shrinkage even if a subsidiary polyol high in poly(oxyethylene) is employed. The catalysts and stabilizer combinations utilized in the examples of this patent would not yield commercially viable systems for making flexible polyurethane foam. Processing latitude and formulating flexibility would be very limited.
Numerous other patents, both domestic and foriegn, disclose and claim various polyol blends but for the most part, none employs polymer polyols and/or else differ in the composition of the formulation such that desirable HR flexible foams having improved processing advantages are not provided. See for example, Japanese patents SHO 57-133112; SHO 57-195113; SHO 57-195725; and SHO 59-100125; U.S. Pat. No. 4,544,678; British Patent No. 1,480,972; U.S. Pat. No. 4,690,955, and the like.
Hence, prior to the present invention high resilience foam formulations were not readily available having the desirable latitude for varying formulation components without adversely affecting processing and desired physical properties. Current HR slabstock systems become deficient in processing as the water level in the formulation is increased to make lower density foams; and/or as the crosslinker level is increased or decreased beyond current limits; and/or as the index is increased or decreased beyond current limits. These limitations restrict the range of foam grades (i.e., density and load) that can be produced and limit the markets/applications in which they have been used.
Prior to the present invention the production of flexible HR foam densities below about 1.8 pcf and/or loads below about 20 pounds/50 square inch, typically required the use of blowing agents such as the halocarbons. However, due to environmental considerations, the current trend is to avoid or minimize the use of such blowing agents in the preparation of foams. Also, production of higher load HR grades has required the use of expensive load building additives that can now be eliminated or greatly reduced under the teachings of this invention.